As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, on the other hand, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and long-sheet type anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
FIG. 1 is a side view typically illustrating the general structure of a conventional representative stacking type electrode assembly.
Referring to FIG. 1, the stacking type electrode assembly 10 is constructed in a structure in which cathodes 20, each of which has a cathode active material 22 applied to the opposite major surfaces of a cathode current collector 21, and anodes 30, each of which has an anode active material 32 applied to the opposite major surfaces of an anode current collector 31, are sequentially stacked while separators 80 are disposed respectively between the cathodes 20 and the anodes 30.
From one-side ends of the cathode current collectors 21 and the anode current collectors 31 protrude pluralities of cathode tabs 40 and anode tab 50, to which an active material is not applied, such that the cathode tabs 40 and the anode tab 50 are electrically connected to a cathode lead 60 and an anode lead (not shown) constituting electrode terminals of a battery (not shown). The cathode tabs 40 and the anode tab 50 are joined in a concentrated state, and are then connected to the cathode lead 60 and the anode lead, respectively. This structure is more clearly illustrated in FIG. 2, which is an enlarged view illustrating the joint between the electrode tabs and the electrode leads.
Referring to FIG. 2, the plurality of cathode tabs 40, which extend from the respective cathode current collectors 21 of the electrode assembly 10, and the plurality of anode tabs 50, which extend from the respective anode current collectors 31 of the electrode assembly 10, are connected to the cathode lead 60 and the anode lead 70, respectively, for example, by welding. The electrode leads 60 and 70 are generally manufactured through a process for punching a metal plate and cutting the punched metal plate into a predetermined size. As a result, sharp edges or sharply angled parts (circle A) may be formed at cut regions 61 and 62 of the cathode lead 60. According to circumstances, burrs (not shown) may be formed at the cut regions of the cathode lead. The sharply angled parts (circle A) and the burrs formed at the ends of the electrode leads may break the electrode tabs 40 and 50, which have a low mechanical strength, during the movement of the electrode assembly due to an external force applied to the electrode assembly.
On the other hand, a pouch-shaped secondary battery is constructed in a structure in which the electrode assembly with the above-stated construction is mounted in a pouch-shaped battery case made of a laminate sheet including a metal layer and a resin layer. In this case, the electrode leads, which are connected to the corresponding electrode tabs of the electrode assembly, are thermally welded to the battery case while the ends of the electrode leads opposite to the joint between the electrode leads and the electrode tabs are exposed to the outside of the battery case. Consequently, the electrode leads, having a predetermined thickness, deteriorates the sealability of the battery case. Furthermore, the battery case may be damaged by the sharply angled parts and the burrs formed at the ends of the electrode leads.
Therefore, there is a high necessity for a technology that is capable of preventing the damage to the electrode tabs and/or the battery case, even when the electrode leads are brought into contact with the electrode tabs and/or the battery case, during the movement of the electrode assembly.